There's lots of quality steel out there. Looks for tubing decals that don't bear the bike manufacturer's name. So if it's a Fuji, you're probably looking for a Tange sticker. A Fuji tubing sticker means that it's house brand and probably some generic hi-ten steel.

Reynolds, Columbus, Tange, and Ishiwata are good tubesets. There are probably others I'm not thinking of.

Look for turkey wing brake levers, that's a signal of a cheap bike boom bike as are shifters up on the stem.

For drivetrain stuff, older SunTour stuff is good, Shimano 105 and 600 are good on older bikes. 600 is now Ultegra and you may even find some stuff marked 600 Ultegra. Most Campagnolo groups are good, though there are some clunkers at the bottom of the range. It's just that Campy's range doesn't go as low as Shimano's.

Look at the finish on the lugs. Until the late-80s all frames were lugged. The mark of quality is typically smooth edges on the lugs and extensive lug shaping (such as bringing them to a long point).

Lookout for 27" wheels. Lots of older bikes in the US and UK were 27"ers and there's nothing wrong with it, but your choices of quality rims and tires are much fewer and harder to come by today.